Analysis of coding tools and improvement of text readability for screen content

Abstract—Current video coding standards perform well for video sequences captured by a real camera. The aperture of the camera’s optical system smooths the content and attenuates higher frequencies. New application scenarios, enabled by the growing number of high bit rate internet gateways, however, make it necessary to take a closer look at the efficiency of such standards in handling artificial content. Remote desktop appli-cations for example often include text parts. As a consequence, these content types contain sharp edges or high frequencies, which are considered less important in natural video and are therefore treated less carefully. The frequent result is an increased occurrence of artefacts or the loss of information that is actually important to the user. This paper gives an analysis of such artificially created video sequences, evaluates the performance of current coding tools for this type of content and proposes a simple, yet effective way to maintain readability of text within video material using only well considered encoder control and without the need of large additional modules. I

Subjective quality evaluation of foveated video coding using audio-visual focus of attention

This paper presents a foveated coding method using audio-visual focus of attention and its evaluation through extensive subjective experiments on both standard definition and high definition sequences. Regarding a sound-emitting region as the location drawing the human attention, the method applies varying quality levels in an image frame according to the distance of a pixel to the identified sound source. Two experiments are presented to prove the efficiency of the method. Experiment 1 examines the validity and effectiveness of the method in comparison to the constant quality coding for high quality conditions. In Experiment 2, the method is compared to the fixed bit rate coding for low quality conditions where coding artifacts are noticeable. The results demonstrate that the foveated coding method provides considerable coding gain without significant quality degradation, but uneven distributions of the coding artifacts (blockiness) by the method are often less preferred than the uniform distribution of the artifacts. Additional interesting findings are also discussed, such as content dependence of the performance of the method, the memory effect in multiple viewings, and the difference in the quality perception for frame size variations